THE FAMILIES AND GENERA OF BATS. 35 



the upper tooth. As the jaws close the cutting edges pass each other 

 with a shearing motion, c 1 working against posterior edge of pm *, c 2 

 against c 1 , c 3 against c 2 , c 4 against c 3 , and so on to the end of the 

 series. At the same time a less important though equally definite 

 action takes place between the innermost cusps of both sets of teeth. 

 This consists principally of the passing of the posterior inner side 

 of mcd 1, 2, and 3 and anterior inner side of ecd 1, 2, and 3 across 

 the inner surface of the three protocones, the. point of the large cusp 

 in each instance fitting closely to the angle between the two small 

 ones. The paraconid of m 2 and m , also comes within cutting dis- 

 tance of the hypocone of to 1 and m 2 when it is large enough to be 

 functional. As the stroke finishes each hypoconid scrapes through 

 the hollow at middle of opposed crown, and finally comes in oppo- 

 sition with inner side of corresponding protocone, across which it 

 passes as the jaw is moved downward and toward the opposite side 

 to take its position for the next stroke. At the same time each 

 protoconid passes through the space at front of its corresponding 

 upper tooth and comes similarly in opposition with posterior heel 

 of the tooth in front, or with its hypocone when this cusp is present. 

 While the full stroke just described is taking place on one side, a 

 somewhat reversed half stroke occurs on the other, the inner surface 

 of the long outer cusps of the lower teeth cutting against the outer 

 side of the opposed inner cusps of the upper teeth, the action between 

 them being the exact reverse to that which takes place near the end 

 of the full stroke. As the recovery for the next stroke proceeds, 

 the rounded convex outer surface of the protoconids and hypoconid s 

 pass through the depressions between the paracones and metacones, 

 while the similarly rounded inner surfaces of the upper teeth pass 

 between the main cusps of the lower teeth, the result being a grind- 

 ing and crushing action which must be very effective in the final 

 trituration of small particles of food. 



The foregoing description of the molars in action is primarily based 

 on the genus Noctilio, in which the molars are large enough to be 

 readily examined and in which their effectiveness of structure is at 

 its maximum. The cutting apparatus is essentially the same in all 

 bats with normal teeth, though its apparent effectiveness is in some 

 instances reduced without any considerable change in the form of the 

 ■cusps. Thus,-in Myotis myotis the protoconids and hypoconids are 

 so long and straight that they are less readily brought in contact with 

 the styles, the stroke apparently losing thereby. In some Phyllosto- 

 midse the lateral motion of the mandible is lessened by the large size 

 of the canines, which in certain genera develop large cutting edges. 

 When this occurs the outer portion of the upper molars appears to be 

 invariably reduced, the corresponding change in the lower teeth 

 showing itself in the lessened transverse diameter of the triangles. 



